The following commit has been merged into the x86/core branch of tip: Commit-ID: 5a9c361a416fc3a3301e859ff09587cc1b933eb8 Gitweb: https://git.kernel.org/tip/5a9c361a416fc3a3301e859ff09587cc1b933eb8 Author: Peter Zijlstra <peterz@xxxxxxxxxxxxx> AuthorDate: Mon, 11 Jul 2022 11:49:50 +02:00 Committer: Peter Zijlstra <peterz@xxxxxxxxxxxxx> CommitterDate: Mon, 17 Oct 2022 16:41:09 +02:00 objtool: Allow STT_NOTYPE -> STT_FUNC+0 sibling-calls Teach objtool about STT_NOTYPE -> STT_FUNC+0 sibling calls. Doing do allows slightly simpler .S files. There is a slight complication in that we specifically do not want to allow sibling calls from symbol holes (previously covered by STT_WEAK symbols) -- such things exist where a weak function has a .cold subfunction for example. Additionally, STT_NOTYPE tail-calls are allowed to happen with a modified stack frame, they don't need to obey the normal rules after all. Signed-off-by: Peter Zijlstra (Intel) <peterz@xxxxxxxxxxxxx> --- tools/objtool/check.c | 74 ++++++++++++++++++++++++++---------------- 1 file changed, 47 insertions(+), 27 deletions(-) diff --git a/tools/objtool/check.c b/tools/objtool/check.c index e532efb..7936312 100644 --- a/tools/objtool/check.c +++ b/tools/objtool/check.c @@ -129,16 +129,13 @@ static bool is_jump_table_jump(struct instruction *insn) static bool is_sibling_call(struct instruction *insn) { /* - * Assume only ELF functions can make sibling calls. This ensures - * sibling call detection consistency between vmlinux.o and individual - * objects. + * Assume only STT_FUNC calls have jump-tables. */ - if (!insn_func(insn)) - return false; - - /* An indirect jump is either a sibling call or a jump to a table. */ - if (insn->type == INSN_JUMP_DYNAMIC) - return !is_jump_table_jump(insn); + if (insn_func(insn)) { + /* An indirect jump is either a sibling call or a jump to a table. */ + if (insn->type == INSN_JUMP_DYNAMIC) + return !is_jump_table_jump(insn); + } /* add_jump_destinations() sets insn->call_dest for sibling calls. */ return (is_static_jump(insn) && insn->call_dest); @@ -1400,21 +1397,18 @@ static void add_return_call(struct objtool_file *file, struct instruction *insn, list_add_tail(&insn->call_node, &file->return_thunk_list); } -static bool same_function(struct instruction *insn1, struct instruction *insn2) -{ - return insn_func(insn1)->pfunc == insn_func(insn2)->pfunc; -} - -static bool is_first_func_insn(struct objtool_file *file, struct instruction *insn) +static bool is_first_func_insn(struct objtool_file *file, + struct instruction *insn, struct symbol *sym) { - if (insn->offset == insn_func(insn)->offset) + if (insn->offset == sym->offset) return true; + /* Allow direct CALL/JMP past ENDBR */ if (opts.ibt) { struct instruction *prev = prev_insn_same_sym(file, insn); if (prev && prev->type == INSN_ENDBR && - insn->offset == insn_func(insn)->offset + prev->len) + insn->offset == sym->offset + prev->len) return true; } @@ -1422,6 +1416,32 @@ static bool is_first_func_insn(struct objtool_file *file, struct instruction *in } /* + * A sibling call is a tail-call to another symbol -- to differentiate from a + * recursive tail-call which is to the same symbol. + */ +static bool jump_is_sibling_call(struct objtool_file *file, + struct instruction *from, struct instruction *to) +{ + struct symbol *fs = from->sym; + struct symbol *ts = to->sym; + + /* Not a sibling call if from/to a symbol hole */ + if (!fs || !ts) + return false; + + /* Not a sibling call if not targeting the start of a symbol. */ + if (!is_first_func_insn(file, to, ts)) + return false; + + /* Disallow sibling calls into STT_NOTYPE */ + if (ts->type == STT_NOTYPE) + return false; + + /* Must not be self to be a sibling */ + return fs->pfunc != ts->pfunc; +} + +/* * Find the destination instructions for all jumps. */ static int add_jump_destinations(struct objtool_file *file) @@ -1519,18 +1539,18 @@ static int add_jump_destinations(struct objtool_file *file) strstr(insn_func(jump_dest)->name, ".cold")) { insn_func(insn)->cfunc = insn_func(jump_dest); insn_func(jump_dest)->pfunc = insn_func(insn); - - } else if (!same_function(insn, jump_dest) && - is_first_func_insn(file, jump_dest)) { - /* - * Internal sibling call without reloc or with - * STT_SECTION reloc. - */ - add_call_dest(file, insn, insn_func(jump_dest), true); - continue; } } + if (jump_is_sibling_call(file, insn, jump_dest)) { + /* + * Internal sibling call without reloc or with + * STT_SECTION reloc. + */ + add_call_dest(file, insn, insn_func(jump_dest), true); + continue; + } + insn->jump_dest = jump_dest; } @@ -3309,7 +3329,7 @@ static int validate_sibling_call(struct objtool_file *file, struct instruction *insn, struct insn_state *state) { - if (has_modified_stack_frame(insn, state)) { + if (insn_func(insn) && has_modified_stack_frame(insn, state)) { WARN_FUNC("sibling call from callable instruction with modified stack frame", insn->sec, insn->offset); return 1;
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